Illuminating device

ABSTRACT

An illuminating device, as for a microscope, includes a light source and a reflecting filter system. The beam of light of the light source undergoes a plurality of reflections in the reflecting filter system. The entering beam of the reflecting filter system has an optical beam offset and/or a change in direction relative to the exiting beam.

The present invention relates to an illuminating device which ispreferably used for a microscope, in particular for a UV microscope oran optical device having imaging optics, and which includes a lightsource and a reflecting filter system; the beam of light of the lightsource undergoing several reflections in the reflecting filter system.

BACKGROUND

Illuminating devices of the type described are known, for example, fromGerman Patent Application DE 199 31 954 A1. This illuminating device isused as a light source and wavelength selection device for a DUV (=deepultra-violet) microscope. Illuminating devices for DUV microscopes mustprovide illuminating light of a narrow illumination wavelength range forwhich the microscope optics are corrected. The illumination wavelengthrange is characterized by the spectral position of the intensity maximumand the half-value width thereof. Known systems for selecting thedesired illumination wavelength range from a spectrum of a suitablelight source, such as a mercury vapor lamp, include both narrow-bandtransmission filter systems and reflecting filter systems. These filtersystems are arranged in the illumination beam path and feed light of theselected to the illumination wavelength range to the microscope asuseful light.

Narrow-band transmission filter systems in the DUV provide peaks havinga very narrow half-value width; however, the maximum transmission and,thus, the maximum value of the peaks, is only about 20% of the inputoptical power present upstream of narrow-band transmission filtersystem. Therefore, narrow-band transmission filter systems do notconstitute efficient wavelength selection devices for DUV light.

The known reflecting filter systems are composed of several reflectingfilters on which the light of the light source is incident at a certainangle of incidence and at which it is reflected. In these reflectingfilter systems, the reflected and thus useful component of the light ofthe selected illumination wavelength range is considerably more than 90%of the input optical power.

In the reflecting filter system known from German Patent Application DE199 31 954 A1, provision is made for an arrangement of reflectingfilters in which the angles of reflection at the individual reflectingfilters are smaller than 30°. This makes it possible to produce ahalf-value width of the selected illumination wavelength range ofsmaller than 20 nm. Using such a reflecting filter system with smallangles of incidence, the optical power exiting the reflecting filtersystem can be about 98% of the input optical power, depending on thetype of reflecting filters used.

FIG. 1 from German Patent Application DE 199 31 954 A1 shows such anilluminating device together with a DUV microscope. In this context, thereflecting filter system is arranged between the light source and theDUV microscope, which by itself requires an enormous amount of space. Ifthe DUV microscope is used as a semiconductor inspection microscope, itmust be installed and operated in a clean room. Since the expenditurefor operating a clean room increases considerably with increasingvolume, the equipment installed there must be arranged in the mostspace-saving way possible, ideally requiring only a small footprint.

It is often necessary to use several illuminating light sources in anoptical system and particularly in a microscope system, the illuminatinglight sources in each case having an illumination wavelength rangeextending from the infrared via the visual to the DUV wavelength ranges.To this end, usually, up to three different light sources along with thelamp housings are integrated opto-mechanically, which can only beaccomplished using a number of deflection mirrors and/or points of beamcombination in the illumination optics and disadvantageously involves anenlargement or increase in the number of optical beam paths.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide anilluminating device in which the spatial dimensions of the illuminatingdevice are relatively small.

The present invention provides an illuminating device including a lightsource and a reflecting filter system. The beam of light of the lightsource undergoes a plurality of reflections in the reflecting filtersystem. The entering beam of the reflecting filter system has an opticalbeam offset and/or a change in direction relative to the exiting beam.

According to the present invention, it was initially recognized that thespatial dimensions of the illuminating device can be reduced byimplementing an optical beam offset. Thus, unlike the exemplaryembodiment from FIG. 1 of German Patent Application DE 199 31 954 A1,there is no need for a linear arrangement of the light source and thereflecting filter system, but rather it is possible for the light sourceto be arranged above, below or laterally offset from the optical axis ofthe microscope. Especially semiconductor inspection microscopes usuallyhave a very large specimen stage. This specimen stage must be capable ofpositioning the now very large semiconductor products—wavers—relative tothe objective lens of the microscope in such a manner that all regionsof the semiconductor product can be inspected photo-optically.Therefore, an arrangement of a light source combined with an optimizedoptical beam path is only possible above or below the microscope stage.As already mentioned, there is not an arbitrary amount of spaceavailable on the side of the microscope facing away from the microscopeoperator.

Thus, the requirements on an overall system with respect to minimizingits spatial dimensions because of the implementation in a clean room arelargely predetermined by the buyer. In this respect, an illuminatingdevice according to the present invention having an optical beam offsetbetween the entering beam and the exiting beam allows an arrangement ofthe illuminating device on the microscope that meets these requirements.

A reduction of the dimensions of the illuminating device canadvantageously also be achieved by a change in direction between theentering beam and the exiting beam of the reflecting filter system.Because of this, it is possible, for example, to arrange a light sourcelaterally next to the upper part of the microscope stand; the lightsource emitting light in a direction extending to the rear, as viewed bythe operator of the microscope. If a change in direction between theentering beam and the exiting beam is implemented, the illuminatinglight which has been selected with respect to the illuminationwavelength range could be laterally coupled into the microscope afterpassing through the reflecting filter system. It can be a veryparticular advantage to combine an optical beam offset and a change indirection between the entering beam and the exiting beam of thereflecting filter system, so that, for example, a light source can alsobe arranged above the microscope stand, for example, in the rear regionof the microscope, as viewed by the user.

In an embodiment, provision is made for the angle of reflection to be atleast nearly identical for each reflection in the reflecting filtersystem. This allows the use of identical reflecting filters, whichadvantageously simplifies manufacture and reduces the production costs.

In another embodiment, provision is made for a further reflecting filtersystem which is arranged in such a manner that it can be switched to thefirst reflecting filter system. This allows the selection of a differentwavelength or wavelength range of the light source using the furtherreflecting filter system, so that the number of required light sourcescan be reduced in a particularly advantageous manner. Specifically, thereflecting filter systems could be arranged in such a manner that thelight of the light source can be guided through either one or the otherreflecting filter system using deflection devices or switchable mirrors.Also provided is the use of one or more 50:50 beam splitters, dichroicbeam splitters, or the like, which simultaneously guide(s) light of thelight source to at least two reflecting filter systems. In this manner,the illuminating device would provide simultaneous illumination withseveral different wavelengths or wavelength ranges.

In an embodiment, the reflecting filter systems are arranged in such amanner that either one or the other reflecting filter system is broughtinto the optical beam path. This could be accomplished, for example,using filter slide blocks in a suitable mechanical guide. This switchingcould be accomplished mechanically and/or by motor power, it beingdesirable for an illumination device for a semiconductor inspectionmicroscope to have a motor-driven switching mechanism.

The switchably arranged reflecting filter systems are particularlyadvantageously configured in such a manner that in each active positionin the optical beam path, the images of the light source each have thesame position and size in the optical beam path. In this manner, thedesign of the overall system can be further simplified in anadvantageous manner.

If the intention is to use the illuminating device for a VIS or IRmicroscope or for a UV or DUV microscope, the light source is arrangedin a housing. In this context, this housing or lamp housing containsdiverse optical components, such as adjusting means, a reflector, and acollector. In this respect, the light of the light source leaving thelamp housing usually has a nearly collimated beam path. The reflectingfilter system or systems could also be arranged in a housing. Inparticular when using the illuminating device in the field ofmicroscopy, a modular design of the individual components, as is usualin this field, is achieved in this manner. In order to mount theindividual components on the microscope, the lamp housing and thehousing of the reflecting filter system or systems have a, preferablystandard, mechanical interface. Thus, the housings of the illuminatingdevice can be easily adapted to different microscopes or other devices,such as slide projectors.

In a preferred embodiment, the light propagates in an at leastsubstantially collimated manner in the reflecting filter system and/orwhen exiting the reflecting filter system. This measure, too, allowseasy adaptation to the beam path of a microscope or of a slideprojector. This also ensures that the light beam, which propagates in acollimated manner, has approximately the same beam cross-section beforeand after a reflection in the reflecting filter system so that in thecase of several reflections in the reflecting filter system, the opticalcomponents must be geared to the same beam diameter or beamcross-section in terms of their spatial dimensions.

In a preferred embodiment, the reflecting filter system containsreflecting filters which are preferably designed as reflecting notchfilters. In this case, a reflecting filter system is provided withreflecting filters of identical design, which are made, for example, ofblack glass and coated by vapor deposition; such a reflecting filterhaving a reflection coefficient of nearly 1 at the wavelength to beselected. Important to semiconductor inspection microscopy is, inparticular, light of the “i-line”, i.e., UV light having a wavelength of365 nm, as well as “DUV” light, i.e., light having a wavelength of 248nm. The reflection coefficient of such a reflecting filter is very lowfor all other wavelengths so that the light of the wavelength that isnot to be selected is suppressed with each reflection at a reflectingfilter. In a concrete embodiment therefore, at least four reflectingfilters are provided per reflecting filter system. After fourreflections, the light of wavelength ranges that are not selected by thereflecting filter system is substantially suppressed so that, using theinventive illuminating device in conjunction with a UV or DUVmicroscope, it is possible to achieve a microscope image that is nearlyfree of color errors.

In an alternative embodiment, the reflecting filter system contains atransparent component. For internal reflection of the light, thistransparent component has at least two boundary surfaces which areprovided with a reflective coating. These reflective coatings could havea characteristic comparable to that of the reflecting notch filters. Inview of multiple reflection in the transparent component, the boundarysurfaces having a reflective coating are arranged opposite each other.

In a preferred embodiment, the transparent component is shaped in such amanner that the boundary surfaces are arranged nearly parallel or in aslight wedge shape with respect to each other. Thus, in the case ofmultiple reflection, a collimated beam shape in the transparentcomponent is possible if the light entering the component alsopropagates in a collimated manner and if the boundary surfaces arearranged parallel to each other. If the boundary surfaces are arrangedin a slight wedge shape with respect to each other, it is possible, bymeans of multiple reflection in the transparent component, to reduce orincrease the beam diameter of the beam that exits the reflecting filtersystem compared to the beam diameter of the beam that enters thereflecting filter system, which advantageously allows adjustment of thebeam shape without further optical components. In this context, thewedge angle of the boundary surfaces is to be selected such that even inthe case of multiple reflections in the transparent component, light ofthe wavelength or wavelength range to be selected is still reflectedwith sufficient efficiency by the reflective coating of the respectiveboundary surfaces.

The transparent component could be substantially made of glass, quartzglass, CaF2, or of Plexiglas. If the intention is for the illuminatingdevice to provide light of the UV wavelength range, the transparentcomponent is substantially made of quartz glass.

The transparent component has entrance surfaces and exit surfaces forthe light of the light source, the entrance and exit surfaces preferablybeing provided with an anti-reflective coating. In this manner, theportion of light that is reflected at the entrance or exit surfaces canadvantageously be reduced to a great extent so that the anti-reflectivecoating allows further optimization of the luminous efficacy of theilluminating device.

In order to adjust the position of the image of the light source to thebeam path of a microscope or an optical device having imaging optics,beam-shaping means are provided in the beam path of the reflectingfilter system or in the housing thereof. These can be lenses or curvedreflective surfaces. Ultimately, therefore, an adjustment to therequirements of the optical beam path of the downstream device canalready be accomplished before the illuminating light selected by thereflecting filter system exits the illuminating device.

Also advantageously, passive and/or active means for cooling areprovided in the illuminating device and, in particular, in thereflecting filter system. The light that is not reflected by thereflecting filter system is usually absorbed by light traps; theabsorbed light being converted into heat. In order for the heat producedin the beam trap not to cause unwanted expansion of the other opticalcomponents or thermal damage, which could ultimately lead to an unstableoptical beam path or to an unstable illumination situation, the providedmeans for cooling actively or passively dissipate the heat to theenvironment. The passive means for cooling could, for example, becooling fins protruding from the housing of the reflecting filtersystem. The active means for cooling could, for example, include Peltiercooling.

Since the light of the wavelength range that is not to be selected issuppressed more effectively by multiple reflection in the reflectingfilter system with increasing number of reflections, provision is madefor at least two reflections in the reflecting filter system in order toselect as narrow a band of illumination wavelengths as possible.

In a preferred embodiment, provision is made for an overall systemincluding a microscope and the illuminating device according to thepresent invention. This microscope could be a UV microscope, a DUVmicroscope, a scanning microscope, a confocal or a double-confocalscanning microscope, or a fluorescence microscope. The overall systemcould, in particular, be a semiconductor inspection microscope and/or asemiconductor-measuring microscope.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is elaborated upon below based on exemplaryembodiments with reference to the drawings, in which:

FIG. 1 is a schematic representation of an illuminating device knownfrom the prior art, which is adapted to a DUV microscope;

FIG. 2 shows a three-dimensional view of a first exemplary embodiment ofan illuminating device according to the present invention, which isadapted to a DUV microscope;

FIG. 3 shows the optical beam path of a reflecting filter system in athree-dimensional view;

FIG. 4 shows the optical beam path of a further reflecting filter systemin a three-dimensional view;

FIG. 5 shows a three-dimensional detailed view of an embodiment of ahousing accommodating two reflecting filter systems;

FIG. 6 shows the housing depicted in FIG. 5 in a different switchingstate; and

FIG. 7 shows a schematic representation of a further exemplaryembodiment of a reflecting filter system according to the presentinvention.

DETAILED DESCRIPTION

FIG. 1 shows a schematic representation of an illuminating device 1together with a DUV microscope 2, as known from the prior art.Illuminating device 1 has a light source 3 and a reflecting filtersystem 4. Beam 5 of the light of light source 3 undergoes severalreflections in reflecting filter system 4. In this context, the angle ofreflection is identical for each reflection in the reflecting filtersystem. DUV microscope 2 features a detector 6 which is designed as a TVcamera. The illuminating light beam is divided by beam splitter 7.Object 9, which is arranged on microscope stage 8, is imaged byobjective lens 10 to detector 6.

FIG. 2 shows an exemplary embodiment of an inventive illuminating device1 that is adapted to a semiconductor inspection microscope which isdesigned as a DUV microscope 2. This illuminating device 1 features alight source and a reflecting filter system; the beam path of thereflecting filter system being shown in greater detail in FIG. 3.

According to the present invention, reflecting filter system 4 ofilluminating device 1 is designed in such a manner that entering beam 11has an optical beam offset 13 relative to exiting beam 12. In thiscontext, entering beam 11 of reflecting filter system 4 is associatedwith light source 3, which is not shown in FIG. 3. After passage throughreflecting filter system 4, the selected illuminating light exitsreflecting filter system 4 in the form of exiting beam 12 and enters DUVmicroscope 2, which is not shown in FIG. 3 either.

Using reflecting filter system 4 from FIG. 3, it is possible to selectlight of the wavelength range of 365 nm±8 nm (i-line). Reflecting filtersystem 14, which is shown in FIG. 4, is used to select DUV light of thewavelength range of 248 nm±7 nm.

Reflecting filter system 4 from FIG. 3 and reflecting filter system 14from FIG. 4 are both implemented in DUV microscope 2 shown in FIG. 2. Inthis context, the two reflecting filter systems are arranged in housing15 in such a manner that they can be switched by motor power. In doingso, either reflecting filter system 4, which is designed to select thei-line, or reflecting filter system 14, which is designed to select the248 nm line, are alternatively brought into the optical beam path as awhole.

FIGS. 5 and 6 are three-dimensional detailed views of the inside of thehousing 15 depicted in FIG. 2. In the case of FIG. 5, reflecting filtersystem 4 from FIG. 3 is brought into the illuminating beam path. In FIG.6, housing 15 from FIG. 5 is shown in an operating position in whichreflecting filter system 14 from FIG. 4 is brought into the illuminatingbeam path. Both reflecting filter systems 4, 14 from FIGS. 5 and 6 areadapted on a plate 16. Plate 16 is rotatably mounted about an axis ofrotation 17 and can be rotated by motor 18. In this connection, plate 16is designed to have two rotational positions, namely one position at 0°,which is shown in FIG. 5, and the other position at 180°, which is shownin FIG. 6. Due to this space-saving, compact, and rugged design, eitherlight of the wavelength 248 nm or light of the wavelength 365 nm can beselected or made available to the microscope as illuminating light usingonly one light source 3. In this context, it should be particularlypointed out that the space-saving design is further facilitated by theoptical path in reflecting filter system 4, 14, the optical path beingfolded upon itself.

From FIG. 2, it can be seen that light source 3 is located in housing19; further light sources (for the visual bright-field and white-lightconfocal modes) are located in the two other housings 20.

Mechanical interface 21 of the housing of the reflecting filter systemis indicated in FIGS. 3 and 4, and also shown in FIGS. 5 and 6. Both themechanical interface for adaptation to microscope 2 and that foradaptation to lamp housing 19 are standard and comply with thedimensions and modes of operation used in microscopy.

From FIGS. 3 and 4, it can be seen that both the light in reflectingfilter system 4, 14 and the light entering or exiting reflecting filtersystem 4, 14 propagate in an at least substantially collimated manner.Reflecting filter systems 4, 14 each contain four reflecting filters 22,which are designed as reflecting notch filters. Accordingly, reflectingfilters 22 from FIG. 3 reflect light of the wavelength 365 nm;reflecting filters 22 shown in FIG. 4 reflect light of the wavelength248 nm.

FIG. 7 shows a further exemplary embodiment of a reflecting filtersystem 4, in which a transparent component 23 is used. In thisreflecting filter system 4, an optical beam offset 13 between enteringbeam 11 and exiting beam 12 is implemented as well. Transparentcomponent 23 has two boundary surfaces 24 which are provided with areflective coating 25. The shape of transparent component 23 is selectedsuch that the two boundary surfaces 24 are arranged parallel to eachother. Transparent component 23 is made of quartz glass. At entrancesurface 26 of transparent component 23, light of light source 3 (notshown in FIG. 7) enters the transparent component. After a total of sixreflections in transparent component 23, the light which has now beenselected with respect to the illumination wavelength range exitstransparent component 23 at exit surface 27. Both entrance surface 26and exit surface 27 are provided with an anti-reflective coating inorder that the smallest possible amount of the light to be selected isreflected at entrance surface 26, i.e., does not enter transparentcomponent 23. The anti-reflective coating of exit surface 27 is alsodesigned in such a manner that the smallest possible amount of usefullight is reflected internally, i.e., in transparent component 23. Inthis manner, loss of useful light due to unintended reflections isminimized.

In the beam path of reflecting filter system 4 shown in FIG. 3,provision is made for beam-shaping means 28 and 29. Beam-shaping means28 and 29 are, on the one hand, a converging lens and, on the otherhand, a diverging lens. In this manner, the position of the image oflight source 3 is brought to the position that reflecting filter system14 has in conjunction with light source 3.

A means for cooling 30 is provided in each of reflecting filter systems4, 14 from FIGS. 3 and 4. This means for cooling 30 is arranged behindfirst reflecting filter 22, which reflects the light of the light sourcefor the first time. Means for cooling 30 is designed to be passive andserves as a beam trap for the light that is not reflected by thisreflecting filter reflecting filter.

Altogether, provision is made for four reflections at the fourreflecting filters 22 of reflecting filter systems 4, 14 from FIGS. 3and 4.

To conclude, it should be pointed out very particularly that theexemplary embodiments discussed above serve only to illustrate theclaimed teaching without limiting the teaching to the exemplaryembodiments.

LIST OF REFERENCE NUMERALS

-   1 illuminating device-   2 DUV microscope-   3 light source-   4 reflecting filter system-   5 beam of light from (3)-   6 detector-   7 beam splitter-   8 microscope stage-   9 object-   10 objective lens-   11 entering beam-   12 exiting beam-   13 optical beam offset-   14 further reflection system-   15 housing of (4), (14)-   16 plate-   17 axis of rotation-   18 motor-   19 housing of (3)-   20 housing of further light sources-   21 mechanical interface-   22 reflecting filter-   23 transparent component-   24 boundary surface-   25 reflective coating-   26 entrance surface-   27 exit surface-   28 beam-shaping means-   29 beam-shaping means-   30 means for cooling

1. An illuminating device comprising: a light source configured toprovide a beam of light; a housing; a first reflecting filter systemdisposed in the housing and including at least four first reflectingnotch filters configured to reflect light having a wavelength of 365 nm;a second reflecting filter system disposed in the housing and includingat least four second reflecting notch filters designed to reflect lighthaving a wavelength of 248 nm; and a plate disposed in the housing andconfigured to selectively, one at a time, bring the first reflectingfilter system and the second reflecting filter system into the beam oflight; wherein each of the first and second reflecting filter systems isconfigured so that the beam of light undergoes at least four reflectionsin the respective reflecting filter system and an entering beam of therespective reflecting filter system has an optical beam offset relativeto an exiting beam thereof the entering beam being parallel to theexiting beam.
 2. The illuminating device as recited in claim 1 whereinthe illuminating device is configured for use in a microscope.
 3. Theilluminating device as recited in claim 2 wherein the microscope is a UVmicroscope.
 4. The illuminating device as recited in claim 1 wherein arespective angle of reflection is at least nearly the same for each ofthe at least four reflections.
 5. The illuminating device as recited inclaim 1 wherein the plate is rotatable so as to enable the selectively,one at a time, bringing the first reflecting filter system and thesecond reflecting filter system into the beam of light so as to select awavelength of light of the light source.
 6. The illuminating device asrecited in claim 5 further comprising at least one of a mechanical and amotor-driven switching mechanism for rotating the plate.
 7. Theilluminating device as recited in claim 1 wherein the light source isdisposed in the housing.
 8. The illuminating device as recited in claim7 wherein the housing has a standard mechanical interface.
 9. Theilluminating device as recited in claim 1 wherein the light propagatesin an at least substantially collimated manner at least one of when inthe reflecting filter system and when exiting the reflecting filtersystem.
 10. The illuminating device as recited in claim 1, furthercomprising a beam-shaping device disposed in at least one of a beam pathof at least one of the first and second reflecting filter systems and inthe housing.
 11. The illuminating device as recited in claim 10 whereinthe beam-shaping device includes a lens.
 12. The illuminating device asrecited in claim 1 further comprising at least one of a passive and anactive cooling device associated with at least one of the first andsecond reflecting filter systems.
 13. A microscope comprising anilluminating device, the illuminating device comprising: a light sourceconfigured to provide a beam of light; a housing; a first reflectingfilter system disposed in the housing and including at least four firstreflecting notch filters configured to reflect light having a wavelengthof 365 nm; a second reflecting filter system disposed in the housing andincluding at least four second reflecting notch filters designed toreflect light having a wavelength of 248 nm; and a plate disposed in thehousing and configured to selectively, one at a time, bring the firstreflecting filter system and the second reflecting filter system intothe beam of light; wherein each of the first and second reflectingfilter systems is configured so that the beam of light undergoes atleast four reflections in the respective reflecting filter system and anentering beam of the respective reflecting filter system has an opticalbeam offset relative to an exiting beam thereof, the entering beam beingparallel to the exiting beam.
 14. The illuminating device as recited inclaim 13 wherein the housing has a standard mechanical interface. 15.The microscope as recited in claim 13 wherein the microscope is at leastone of a semiconductor inspection and a semiconductor measuringmicroscope.